The present invention is directed to an open headed medical implant and, in particular, to a closure for closing the head of an open headed bone screw, hook or the like.
Bone screws are used especially in spinal surgery to support and position various implants needed to repair a spine that has suffered injury, illness or genetic defect. Bone screws of this type are screwed into the vertebrae of the spine and have a head that projects outside the bone which receives other implants, such as rods, that extend along the spine. Bone screws are of two general types which are either open headed or closed headed. Hooks and certain other implants also sometimes have open heads. The present application is directed to open headed bone screws and related implants such as hooks and the like that have such an open head to receive another implant.
In open headed bone screws and related implants, the head includes two upright arms that form a channel therebetween. The channel is sized to receive a rod or the like and is open to make it easier to place the rod in the head. The rod must then be tightly held or locked in the head to prevent relative movement between implants after the surgery. To hold the rod in the head, plugs have been used that are screwed into threads on the interior surfaces of the arms.
The present invention is directed especially to improvements in such plugs or closures that make them easier to insert in the head, that better ensure that the plug effectively secures the rod so that the rod does not later slip, that allow the plugs to be easily removed should the overall implant system require rearrangement and which provide a comparatively low profile, so as reduce trauma and irritation to the surrounding tissues of the patient.
A closure is provided for an open headed implant, especially a bone screw or hook for use in spinal surgery. The closure has a cylindrical shaped body with an axis of rotation. The body has a radially outer surface that is threaded with a thread that is sized and shaped to be received in mating threads on interior surfaces of arms of the implant head. The closure is operably threaded into the head of the implant to capture a rod or other part of an overall spinal support system. The closure captures and locks such a rod in position relative to the implant to prevent rotation or axial movement between the joined parts.
The closure body has a top surface and a bottom surface with a plurality of bores extending parallel to the axis of rotation into the body from the top surface. The bores are positioned in spaced relationship to one another and to the axis of rotation. The bores are sized and shaped to cooperatively mate with posts on a tool to allow removal of the closure from the implant after insertion, should such be necessary. In some instances the tool may also be used to install the closure in the implant.
In one embodiment the closure also includes a break-off head centrally mounted by a neck on the top surface of the body. The break-off head is adapted to receive a socket tool and be rotated thereby during installation. The break-off head is also designed to break from the body at a break-off point or location which is preferably whereat the neck intersects with the top surface of the body; when a preselected torque is applied to the break-off head. When the break-off head is broken away, the bores that are adapted to mate with a removal tool become exposed.
In a second embodiment the body includes a central threaded bore that receives a set screw. The body is then used for capture of a rod or the like and the set screw is used to lock the rod or the like in position relative to the implant.
In a third embodiment, a body includes both a break-off head and a central threaded bore that is covered by the break-off head until the head breaks away, after which the threaded bore is exposed at the top surface of the body to receive a set screw.
Therefore, the objects of the present invention are: to provide a closure for an open ended implant that provides a plurality of spaced bores that are offset from an axis of rotation of the closure and that cooperate with a tool to allow removal of the closure; to provide such an implant having a closure with a break off head for mating with an insertion tool for inserting the closure into the implant; to provide such an implant wherein the removal bores are not accessible for effective access, when the closure is in the implant until the break-off head is broken away; to provide such an implant having a closure wherein a closure body has an axially centered threaded bore and including a set screw sized and shaped to be threaded into and extend from the bottom of the closure threaded bore when fully inserted therein; to provide such an implant having a break-off head joined by a neck to a body of the closure and centered on a top of the closure with the body also having a central threaded bore that extends from a bottom to the top of the closure body, but the threaded bore is unaccessible at the top of the body until the break-off head breaks from the body; to provide such an implant that strongly grips a rod or the like received in the implant and that provides a relatively low profile; and to provide such an implant and closure therefore that is relatively easy to use, comparatively easy to produce and is especially well suited for the intended use thereof.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.
The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.